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Concept
The Simple Multifunction Beacon concept designed by N7BHC goes one step beyond a simple transmitter beacon. They are based on multimode radios with an amplifier and keyer. The system operates as a beacon most of the time. When a band opening is reported, the local operator can turn off the beacon and use the same equipment to work DX. This allows two-way contacts to be made over the same equipment. The design on this web page profiles a VHF beacon operating on the 144 MHz 2m amateur band, but the principles are directly applicable to a 430 MHz 70cm beacon as well, or even to other bands.DesignThe design selected is fairly simple. There are undoubtedly more efficient modes and equipment to use. However, simplicity and reliability are considered extremely important. Another overarching consideration is size and weight as they shipping costs to remote locations can be very expensive.The design is based around an all-mode 2m radio. This allows it to be used with a simple memory keyer circuit to generate a CW beacon running at about 12 wpm Morse code. The radio can also be used as an SSB or CW transceiver when the band is open. The radio drives a 160 watt amplifier. The drive level on the radio is reduced in beacon mode to run the amplifier at the 80-100 watt output level. This keeps the amplifier cool and increases its reliability and MTBF. The radio is switched to full power in operate mode to gain the extra 3dB output power. A switching power supply rounds out the equipment lineup. The whole assembly is assembled on a 3U standard 19" wide rack shelf, about 20" deep. The antenna is chosen based on the location. Beacons on a continental coast use yagi antennas as they are purposefully beaming across the ocean. Beacons on mid-oceanic Islands need omni-directional or bi-directional antennas, depending on where the target locations are.Equipment Selection
- Radio. The radio forms the basis of the simple multifunction beacon.
- It needs to be capable of operating in CW as a beacon, and in CW, SSB, FM, or digital modes when used for two-way communications. This means an all-mode radio is required. Models are available for both mobile and base station installation. The mobile radios are used in this beacon design to cut down on weight and size. Base station radios would be adequate or even better performers, and can be used if size and weight are not factors to be considered.
- Another consideration is that the radio needs to be a VHF use only model. There is a risk that if an all-band radio covering HF is provided on a beacon shipped to a remote location, it may eventually be removed from the beacon and put to use on HF, which would mean the beacon would be taken off the air.
- The radio and amplifier selection need to be considered together. the radio at is at maximum power should drive the radio to full output in two-way operation. The radio should also have a low power mode which can be adjusted to drive the amplifier to the desired output level in beacon mode.
- Several models of radio were considered for the beacon design, and several were tested before selecting the Kenwood TR-751A for the 2m band. The TR-851A is the 70cm equivalent. The radios that were considered are:
- Kenwood TR-9000 and TR-9130. These radios were tested and functioned well in beacon mode. They are older models, and the receivers are not as good as more modern radios. They do require a good receive preamp when used in two-way mode. The biggest downfall of these units is that they lose their programmed frequency and mode memory when DC power is removed. The memories would need to be reprogrammed after every power failure at the site, requiring a local operator who can make repeated trips to the beacon site. If the beacon is not monitored often, it may even be off the air for weeks or months before the problem is found and rectified
- Kenwood TR-751A. These radios are the next generation after the 9000 and 9130. they have very good receivers, and retain their memories if power is removed. The radio has adjustable low and high power settings. It also provides a relay to key the amplifier, eliminating relay chattering in the amplifier. This radio is also readily available on the used market at very reasonable prices.
- Kenwood TM-255A. This would probably be the ideal radio for the beacon. It has excellent sensitivity, and was the final generation of 2m all-mode single band radios produced. However, it is quite scarce on the used market, and sells for 50-100% more than the TR-751A. It is also larger, making integration onto the 19" rack shelf more difficult. The TM-455A is the UHF version. This radio was not tested for this application, but one was used for several years in my Land Cruiser for mountain-topping with great success, and I am very familiar with the 255 and 455 models.
- Icom IC-260A and IC-290A/E/H. These radios are of the same generation as the Kenwood TR-9000 and TR-9130. They also lose programmed memory data if power is removed, and were therefore not considered suitable
- Yaesu FT-480R. This is another pretty good performed that I have used in years past. It is of the same generation as the TR-9130 and IC-290A. It does not lose its memories of power is removed, but it only puts out 10 watts and is fairly large, making mounting difficult in the rack-mount shelf configuration chosen.
- Keyer. The keyer's function is to generate the beacon sequence. The simple beacon transmits CW, so a simple memory keyer would suffice, with the radio operating in CW mode. An improved beacon would use both JT-65 digital mode and CW on alternate sequences. The JT-65 mode would provide the weak signal enhancement of the mode, while CW could be received by many more operators not equipped to decode the digital modes. One additional complication of the JT-65 mode is that the keyed sequence needs toe be transmitted at precise time slots. That would increase the complexity and cost of the entire beacon. The simple, CW keyer is the chosen solution on these simple multifunction beacons.
- Several CW memory keyers such as the PicoKeyer were evaluated. While they did the job, setup required a CW key or paddle. They did work, and are viable options.
- The ID-O-Matic was selected as it is designed with beacon operation as one of its modes. It is programmed via an RS-232 serial port, and can be built in about an hour. Dale Botkin at Hamgadgets provides excellent technical support.
- Amplifier. Several models were considered. Reliability and ruggedness were vital for beacons installed in remote locations. As the amplifiers considered were designed for intermittent service, external fan cooling is required. The FCC limit in the US for unattended beacon stations is 100 watts output, so 160 watt amplifiers were selected. The radio's low power output is adjusted to provide the correct drive required for the amplifier to operate at the 100 watt output level. This also helps the amplifier run cooler, further increasing reliability. Two amplifiers were ultimately selected as being suitable.
- rfConcepst 25/160 watt models. There are several models available. The most commonly used is the rfc 2/315. Some models do not have external hard PTT keying. This is required for reliable keying, especially at low CW speeds. A weak point on these amplifiers is the rear panel fuse holder which makes poor contact to the fuse, leading to excessive slow heating of the fuse and subsequent failure. Research has shown that the fuse holder cap easily exceeds 80ºF above ambient air temperature after just a few minutes of operation. The fuse should be jumpered internally and external fusing installed.
- Mirage B2516G. Earlier models of this amplifier are more reliable and better built than the newer ones. The fusing on these amplifiers is internal on the circuit board. While the fuse holder makes a much better connection to the fuse, and generates much lease heat on the contacts, it should be jumpered internally and external fusing employed. This again is in the interest of reliability and ease of field maintenance.
- Power Supply. The radio and amplifier require 35 Amps at 13.8 volts DC when transmitting on high power. A PSU of 45-50 Amps provides enough reserve capacity to operate reliability . While a linear supply is very capable of meeting the power requirement, a switching supply was chosen to reduce the weight for overseas shipment. A 45 Amp MFJ power supply was selected.
- MFJ-4245MV. This power supply provides 40 Amp continuous and 45 Amp surge current capacity at 13.8 volts. They have proven very reliable over many years of use with not a single failure experienced. An external switch selects either 110 or 220 VAC input. Metering indicates the supplied voltage and current draw. Two fans cool this supply well even in moderately high power beacon use. The exhaust air is quite cool. Careful positioning of the power supply directs the exhaust air across the radio heatsink, doing double duty in cooling the power supply and radio.
Assembly
The simple multifunction beacon can built onto any suitable frame, or even left on a desktop. The physical layout ultimately chosen is a 19" rack shelf, 5.25" high and 18" or more deeper. This allows the entire bacon to be assembled in a compact package with all components anchored in place, increasing reliability and simplifying shipping and installation. Locations without a rack to mount the beacon in can easily manufacture a metal or wood cabinet to house the rack shelf.
- Rack Shelf. The standard design frame is a 19" vented rack shelf. A 3U 5.25" high shelf makes a compact assembly. A 4U 7" high shelf would offer additional top clearance for better cooling in hot environments. The shelf needs to be at least 18" deep to accommodate the depth of radio with the power supply behind it. The venting slots make installing the amplifier and other equipment very simple with self tapping sheet metal screws inserted from the bottom.Rack front panel. A vented front panel protects the equipment while allowing reasonable airflow. Cutouts are made to go around the radio and amplifier. The cutouts are made larger than the radio and amplifier by 1/8" to 1/4". The sharp metal edges of the cutouts are covered with a rubber or plastic edge guard. I have found the outer vinyl covering of 1/4" coaxial cable to be a very good low-cost solution. Slice a length of coax down its length with a sharp knife or razor blade. Cut to length with 45º beveled corners and slide over the sharp metal edge. The keyer on-off switch, CW key jack, and a microphone hanger are attached to the front of the rack panel.
- Layout. The photo to the right shows the overall layout. The radio is on the front right, with the power supply on the right rear. The amplifier is on the front left, with DC power distribution at the left rear. The keyer location is not critical, but is usually nestled near the front between the radio and the right edge of the rack shelf to facilitate the Keyer On/Off switch and an external key jack if desired.Radio. The radio is mounted on the front right side of the rack shelf, and has a few small modifications to make it easy to adjust some internal controls when fixed inside the rack shelf.
- It is positioned so the front panel metal work is 1/8" in front of the rack front panel ears. It should be mounted a few inches from the side wall of the rack shelf to allow for cooling. Occasionally the radio's original clam shell mobile mount can be found and used, as pictured here. Most of the time it is not available, in which case simple aluminum L-brackets are used to support the radio. The height of the radio can be optimized when using the L-brackets so that the middle of the heatsink on the rear panel is the same height as the middle of the power supply fan.
- There are three internal trimmers that may need adjustment from time to time. Drilling three small holes in the top cover of the radio makes these accessible without having to remove the radio from the rack shelf, and remove the top cover. The photo to the right shows these holes. They are for:
- CW Sidetone level. Some locations are manned, and the continual sound of the CW sidetone appears to not be universally appreciated.
- Break-In delay. Adjust this control so that the radio does not chatter between receive and transmit between characters while transmitting.
- Low Power Drive level. Adjust this control so that the drive produced in low power drives the amplifier to the desired output power. Most amplifiers need about 9-10 watts to produce 100 watts output.
- The TR-751A provides a relay closure to key the PTT line of an external amplifier. The 4-pin connector is very hard to find these days, and most of the time one needs to be manufactured. Fortunately this is quite easy. Here is the process I use.
- Remove two pins from a DB9 male connector. Apply heat with a soldering iron until the plastic softens, and pull the pins out with a pair of needle nose pliers.
- Solder a length of hookup wire to each pin.
- Support the radio exactly vertically with the face down.
- Place a piece of masking tape across the rear panel accessory socket.
- Spread a thin layer of Vaseline or silicone grease across the tape over the area of the connector.
- Push the two pins with wire previously described through the masking tape and into their two pins. Be sure to use the correct two pins.
- Modify the plastic shell from a 1/8" phone plug by cutting the narrow end off, or find some other length of 1/4" plastic tube about 3/4" long. Feed it down over the wires from the two pins.
- Mix up some 5-minute two-part epoxy. Carefully drip it down into the connector shell while holding the shell firmly against the masking tape to prevent leakage out the bottom. I use a toothpick for this process.
- After 5 minutes, the epoxy will have set well enough to stay in place without holding the connector shell. Let it rest another 5-10 minutes, then pull it off the rear of the radio.
- Remove the masking tape. The connector is now finished.
- Amplifier. The amplifier is mounted on the right front of the rack shelf. It requires a small modification to operate reliably in long-term beacon use.Mounting. The amplifier draws cooling air in through vents on the bottom and side. To enhance cooling, replace the rubber standoff feet with larger 1/2" high self-adhesive feet. The amplifier is secured to the rack shelf with self tapping metal screws that come through the slots on the rack shelf and screw into the narrow slots on the bottom of the amplifier. If your amplifier does not have vent slots on the bottom, remove the amplifier cover, and position it in place on the rack shelf. Observe where components are located in the amplifier, and then drill four holes through the shelf slots and up into the amplifier case. Alternatively, L-brackets that secure to the screws on the side of the case to the heatsink could be used.
- Fuse. The fuse holders and fuses on the amplifiers are weak points. In high duty cycle extended operation, the fuses tend to age quickly and fail after 1-3 months. On the rfc amplifiers, the poor fuse holder-fuse connection has a little more resistance than desirable. This causes additional heating of the fuse holder and fuse. Temperatures of more than 80ºF above ambient on the back of the fuse holder have been measured after just 10 minutes of operation. The solution is to jumper the internal fuse holders and use an external fuse, or better yet, a circuit breaker. The beacons built at N7BHC use 30 Amp magnetically tripped circuit breakers. These are more reliable than the thermally tripped breakers in this application. Like everything else, they were purchased off EBay.
- Cooling. The amplifiers are not designed for extended, high duty cycle operation. Although the CW transmission is about 30% duty cycle, and 15 second receive periods every minute allow additional cool down time, the amplifiers still run hot, shortening the component life. Additional cooling is provided by two 80mm muffin fans, The fans use ball rather bearings for long, quiet operation. They are run at 13.8 volts off the primary supply. The
- amplifier heatsink runs at less than 5ºF above ambient air with two fans. The fans are glued to each other with superglue, and then superglued to the heatsink, blowing air down onto the heatsink. Fan guards are attached to protect prying fingers and prevent any wires or tools from falling into the blades.Keying. The amplifiers should be hard keyed for PTT rather than rely on RF keying. The Mirage amplifiers use a closure to ground. The rfConcepts amplifiers can either use a ground or +12 volt line for keying. Set the jumper in the rfc amplifiers to use ground for keying (move the wire to the (-) pin internally). This PTT line is keyed by the relay output from the TR-751A,
- Preamp. The preamp is normally left OFF to avoid wear on the preamp relay. It also affords an extra level of protection from nearby static discharges while receiving. The preamp is turned on when the beacon is being used as a standard radio to work DX.
- Keyer. The ID-O-Matic keyer kit is very inexpensive and easy to build. Here are few extra pointers.
- Care must be taken to avoid static discharge while handling the FETs and the PIC processor.
- Use an external 10K ohm trimpot in line with the speaker to reduce the sidetone level.
- If the keyer does not operate properly, check the settings with the programming PC. Incorrect settings in the additional parameters shown by setting Repeater (Y) can prevent operation, even if the Repeater (N) setting is used.
- One can use the settings for "Beacon" mode, but there is an even simpler setup suggested by Dale at HamGadgets. The settings I use on my the ID-O-Matic keyes is shown below.
- ID Time 15 (15 seconds Rx time between beacon transmissions)
- Yellow time 0
- Blink time 0
- ID Msg N7BHC/B EM95QA N7BHC/B EM95QA N7BHC/B EM 95QA :15: (call and grid 3x, 15 second carrier)
- Beacon Msg (blank)
- Alternate Msg (blank)
- Auto CW ID Y
- CW Speed 13
- ID Audio Tone 702
- Repeater N
- The keyer is typically installed between the radio and the left side of the rack shelf. This is convenient for external wiring to the on-off switch which is in the DC supply line.
- The only output used is the CW keying line (pin 5) and Ground (pin 6).
- An front-panel jack can be wired in parallel with the output of the keyer to allow the use of an external key for CW operation.
- Power Supply. The MFJ-4245MV power supply is mounted on the right rear of the rack shelf. It is mounted facing the rear of the assembly. This permits easy access for viewing and wiring. In addition, it directs the exhaust air onto the radio's heatsink.
- Mounting is accomplished with two self-tapping sheet metal screws coming through the rack shelf slots onto existing holes on the bottom of the power supply.
- The power supply is positioned so that the front panel attachment lugs do not extend beyond the rack shelf.
- The AC power cord can push up against the radio heatsink. Either position the power supply and radio to avoid a conflict, or use a right-angle AC power plug.
- Set the power supply to the correct AC input voltage.
- Wiring. There are three categories of wiring on the beacon; DC power, keying, and RF.
- The DC wiring is the most complex part of the wiring. All power is run from the large front panel lugs on the power supply to a power distribution area behind the amplifier where all devices are individually fused.
- The 8 AWG black negative lead goes to a large bolt mounted vertically from the bottom of the rack shelf. The bolt is first secured directly to the chassis with a nut. The negative lead with a lug goes above the first nut, followed by an 8 AWG lead to the amplifier, an 8 AWG negative lead to the radio, and smaller wires to the keyer and amplifier fans. Each lead terminates in a lug. A lockwasher and second nut secure the negative power leads.
- The 8AWG red positive lead goes directly to the lower bolt on the 30 Amp DC circuit breaker. Another positive lead with lug leads from this bolt to the DC fuse block. The circuit breaker is just for the amplifier.
- An 8 AWG red wire from the top of the amplifier's DC circuit breaker goes directly to the amplifier. If using an rfc amplifier, the four pin Cinch-Jones connector is configured to use two pins for positive and two for negative. Wire both in parallel to reduce the voltage drop going to the amplifier.
- An 8 AWG red wire goes from the lower (input) bolt on the circuit breaker to the DC fuse panel. This fuse panel uses blade automotive fuses and a holder, both available from auto parts stores.
- A 10 Amp circuit breaker is used for the radio, 3 Amps for the fans, and 1 Amp for the keyer. Individual wires go to the radio, keyer, and a single wire feeds the two fans which are wired in parallel.
- The keying wiring connects the keyer and front panel key jack to the radio, and the radio to the amplifier.
- The keyer outputs on pins 5 and 6 are CW keying and ground. These go to the Key input on the radio, a 1/8" mono plug.
- A 1/8" mono jack can be mounted on the front panel if an external key will be used to operate CW. It should be wired in parallel with the keyer output lines.
- The TR-751A provides a relay closure to key the amplifier. This requires a very hard to find 4-pin connector on the radio. Instructions were provided above on building a connector if necessary. The amplifier side uses an RCA phone connector.
- If a different radio is used which does not have a relay output, it may have a PTT line that goes low on transmit which could key the amplifier. In addition, the keyer has a PTT output (pin 4) that can be used to key the amplifier directly.
- The RF wiring is just a cable from the radio to the amplifier. My preference is to use an RG-142/U double-shielded teflon cable.
- The antenna can connect directly to the amplifier output or through a wattmeter.
- The DC wiring is the most complex part of the wiring. All power is run from the large front panel lugs on the power supply to a power distribution area behind the amplifier where all devices are individually fused.
- Surge Protection. The two cables to provide surge protection on are the AC power line and the antenna lead.
- AC surge protection can be a god quality consumer grade protector such as an APC product at the least. A better solution would be an ICE 330 or 331 (110 or 220 vlts AC).
- RF surge protection should be installed at the building entrance. A PolyPhaser IS-50NX would be a good solution. The ICE 302 would be even better.
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- Coastal - Unidirectional
- Yagi
- Yagi array
- Mid Ocean - omni or bi-directional
- Loop based
- H-quad-bay
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